The basic premise that he puts together is that consciousness, the actual thought process where we think about what we are doing, is a very slow inefficient process. His estimate, based on several experiments, is that consciousness is limited to processing about 20 bits/second. Compared to the chips of today which are up in the gigahertz range (billions of bits/second), it seems like a truly paltry number. How can we reconcile this with our known ability to outperform computers at many tasks?
Norretranders postulates that most of the work is done at a subconscious level. Nothing too surprising, there. But what was interesting to me was the approach he used. In his theory, the whole point of the subconscious parts of the brain is to reduce the information flow into and out of the brain down to a rate which our feeble 20 bits/sec consciousness can handle. He points out that we perceive about 12 million bits/second (10 million from vision, 1 million from touch, and the rest scattered among the other senses). That's an enormous amount of information to process. But when we look around, we don't see 10 million pixels. Looking from my computer chair, I see my computer, my desk, the windows of the room, etc. He calls this phenomenon chunking information into symbols. To quote him, "symbols are the Trojan horses by which we smuggle bits into our consciousness."
In other words, our subconscious does a truly amazing amount of processing to reduce the 10 million bits we see to the 10 or so objects we actually perceive at any one time. And since we generally focus in on only one object at a time, our consciousness can now handle the bit flow rate. This is why it takes us so much work to deal with something we have never seen before - our brain is desperately trying to cope with the new input. It also explains a lot of what babies are doing for the first year of their life - developing the preconscious mechanisms to handle this overwhelming onslaught of information.
One example I use to illustrate this point that I thought of while reading this book was checking your blind spot while driving in traffic. You quickly glance over your shoulder, then you look straight ahead again. When you looked back, there's all sorts of things in your vision: the rest of your car, other cars on the highway, scenery off to the side of the highway. What your consciousness processes out of all that, though, is one bit - is there a car in my blind spot or not? And it takes a while to process that - there have been many times when I'll initiate a lane change, glance over my shoulder, continue with my lane change, before my consciousness catches up and starts screaming that there was a car in the blind spot.
Similarly, because of the poor information capacity of consciousness, there's an equally amazing expansion of information on the output end as there is compression on the input end. When we do an action, we do not try to control each muscle, or even each limb. We just think "Walk forward", and lower parts of the brain issues the proper commands. This is why it takes so much effort to learn a new action in a sport - you are having to think about moving each limb in a precise way. Later on, once your subconscious has been trained, it's a matter of just issuing the command "Go spike that volleyball", and your body gauges things, jumps high in the air, and coordinates a tremendously complex physical motion involving the legs, arms, and torso to spike that ball down. It also explains the phenomenon that all athletes have experienced - when we screw something easy up, and say "I had too much time to think about it" - Norretranders postulates that this is because the process happened slowly enough that our consciousness got into the loop and tried to control things.
One other interesting result of consciousness being slow is that it explains reaction times. Any time we have to make a conscious decision, it is going to be a slow process. However, if it is wired into the preconsciousness, then reaction can be instantaneous; for instance, if we touch something very hot, we don't wait to think "Ow!" before we move our hand - our hand flinches away, and we're dancing away in pain even before we say "Ow, that hurt!" A cute story from George Gamow about Niels Bohr that Norretranders includes illustrates the same point: "He [Bohr] developed a theory which explained why the hero is quicker and manages to kill the villain despite the fact that the villain is always first on the draw. ... As the hero never fires first, the villain has to decide when he is going to shoot, and this hampers his movements. The hero, on the other hand, acts reflexively and snatches his revolver quite automatically the instant he sees the villain's hand move. We disagreed on this theory, and the next day we went into a toy store and bought two revolvers in western holsters. We shot it out with Bohr, who played the hero. He 'killed' all his students." Norretranders would say that the villain has to involve consciousness which is tremendously slower than the preconscious.
I haven't even gotten to Norretranders explanation of the half-second delay in consciousness (which I need to re-read so that I can explain it better), or exformation, or any of the other fascinating concepts in this book. I highly recommend it obviously. It's a good read, with lots of interesting results that make you think about what how your brain actually works.